Furnace

ABSTRACT

A furnace for melting material and for holding molten or liquid material at elevated temperatures and consisting of a pot heated directly by banks or arrays of gas-fired infrared burners normally closely spaced from and directed at the outer surface of the pot. The banks of burners are movable toward and away from the pot for easy inspection, maintenance, and adjustment, even during operation.

[451 May 29,1973

United States Patent Pearch Patented May 29, 1973 2 Sheets-Sheet 2INVENTOR.

FURNACE BACKGROUND AND SUMMARY OF THE INVENTION Casting and heattreating operations, among others, require means for melting materialand for holding sub- 4stantial quantities of molten or liquid materialat elevated temperatures. For example, in die casting, quantities of 500pounds or more ofaluminum at temperatures of approximately l,200 F. ormore must be maintained close to the desired temperature and readilyavailable to the dies. In heat treating processes such as soaking, largequantities of salt bath at temperatures in the l,200 -l,300 F. range arenecessary and must be maintained within close temperature limits.

Conventionally, reverberatory-type furnaces are used for the heating andholding applications mentioned. Such furnaces are generally fixedstructures which include ponderous amounts of bulky refractory material.Although widely used heretofore, such furnaces have numerousdisadvantages.

The space required and weight involved seriously reduce their mobilityand flexibility of application. In addition, by virtue of the mass ofheat-absorbing material involved, response time to temperature change isslow and resulting regulation of temperature, poor.

In reverberatory-type furnaces, the molten substance or heated liquid orpot containing the substance or liquid is exposed to direct flame and/orcombustion products. Further, such furnaces typically are very noisy andprovide an undesirable acoustic environment for persons required toattend to be in the neighborhood of such a furnace. Another disadvantagesometimes experienced is the non-uniform heating of the pot or crucibleholding the material to be heated with attendant hot spots and shortenedpot life.

The nature of the construction of a reverberatory furnace made ofsubstantial amounts of refractory brick,

, for example, limits inspections, increases costs, and

makes maintenance difficult. Finally, low heat transfer efficienciesresult in high fuel consumption and much heat is lost up the flue.

This invention contemplates a furnace comprising a pot or crucible whichis heated solely by a plurality of quite-operating, gas-fired infraredburners. The burners are supported with their radiating surfaces facingand normally closely spaced from the wall of the pot or crucible. Theycan be arranged in any desired pattern and spacing from the pot wall andfuel and air input to each can be individually controlled to achieve thetemperature distribution and balance desired and to accommodate the sizeand shape of a paritcular target area.

The burners are mounted in banks or arrays on movable supporting frames.Pre-mixed gaseous fuel and air is supplied to individualor individualsets of burner radiant elements from a distribution and supply manifoldsystem, including a branch manifold associated with each frame-supportedarray of burners. In order to provide complete and ready access to allsides of the burners, and particularly to the infrared radiatingsurfaces, the supporting frames are pivotally supported for swingingmotion generally about one side thereof and toward and away from thewalls of the pot.

When the frames are in position for operation of the furnace, theburners are supported in a predetermined pattern and supplied fuel andair in predetermined and controllable amounts with their radiatingsurfaces spaced a desired distance from the wall of the pot. Forinspection and maintenance, the frames are swung away from the pot sothat the radiating surfaces of the burners are moved away from the potand exposed for inspection and adjustment or repair. The connectionbetween each associated branch manifold and the distribution and supplymanifold system preferably provides relative movement as required by theswinging motion of the burner supporting frame without leaking thegaseous fuel and air mixture it carries and permits the supportedburners to be swung away from the pot and inspected, even while they areburning.

The burners preferably used in the furnace of this invention havelimited and discreet areas of burning and radiating surface suppliedwith a mixture of gaseous fuel and air from underlying low pressurechambers substantially coextensive in area. The low pressure chambersare separated from other and adjacent low pressure chambers. Each lowpressure chamber is supplied from a high pressure distribution manifold,preferably through an adjustable orifice. The high pressure distributionmanifold is positioned on the opposite side of the burner from theburning and radiating surface and away from the pot when the burners arein an operating position so that the distribution manifold is maintainedas cool as possible.

The burners are preferably provided with radiating surfaces comprised ofone or more refractory tiles such as, for example, tiles disclosed inU.S. Pat. No. 3,216,478. The anti-backfiring properties of these tilescontribute to the safe operation of the furnace. Even in the event anunlikely backfiring or a burner element or of an inadvertent rupture ofthe radiating surface of a burner, however, the amount of gas readilyavailable and near hot surfaces is minimized by the limited extent ofthe low pressure chamber and, thus, tends to reduce the possibility ofany massive pre-ignition explosions.

Further advantages enjoyed by this invention are quiet operation andelimination of the offensive combustion noises of other designs. Thereis a substantial space saving due to the compact design and absence ofany type of fire brick structure. The furnace holds a minimum ofresidual heat and thus permits close control of temperature without theusual overshooting, even when using off-on controls.

Finally, the burners permit high heat transfer efficiency resulting inlow exhaust temperature, reduced operating costs, and conservation ofcritical fuel. The open side of the pot is shielded from the burners insuch a way that there is no contamination of the molten bath due toexposure of combustion products, and no pollutl ants from the contentsof the pot are carried away in the combustion products of the burners.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is an overall perspective viewof a furnace ernbodying this invention;

FIG. 2 is a perspective view of the furnace shown in FIG. l with partsof the cover or jacket removed or broken away;

FIG. 3 is another perspective view of the furnace shown in FIG. l withone of the sides of the burner supporting frame swung away from the sideof the pot;

FIG. 4 is a transverse section through the furance of FIGS. l, 2, and 3,taken in the plane of line 4-4 in FIG. 2; and

FIG. 5 is a partially sectioned perspective view of one of the burnerscomprising the arrays of burners in the furnace of FIGS. 1-4.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT FIGS. 1, 2, and 3,similar views of a preferred ernbodiment of this invention, show afurnace with various of its elements covered and exposed and with itsmovable parts in different operating positions. The central element ofthe furnace comprises a pot 10 made of any material suitable forwithstanding the temperatures involved and for containing and holdingthe substance to be heated. For high heat input, the pot is preferablyof a shape having a high proportion of flat surfaces such as aparallelepiped. As shown in FIGS. 1-3, the pot has a generallyrectangular and open upper face. Pot 10 is preferably longer than it iswide to provide two substantially parallel large-area flat surfaces.These two largearea surfaces, together, preferably comprise more thanhalf of the total surface area of the pot. Other pot shapes may be used,but, in high input applications especially, it is desirable for thegreater enjoyment of the advantages of this invention to use a pot shapewhich provides a high ratio of pot surface area to volume.

Pot l is provided with an outwardly-turned edge or rim l2 at its upperperimeter which permits the pot to be suspended and supported in asimple frame structure 13. The particular design of the frame forms nopart of this invention. As shown, a simple structure of angles,channels, and tubes, and adapted to support the pot is suitable.Additional support may be provided by resting the bottom of the pot onrefractory blocks, for example. This is especially desirable withlow-strength crucibles.

Banks or arrays, indicated generally at B, of infrared gas burners 14are arranged and positioned with their radiating surfaces directedtoward and normally closely spaced from the large-area side surfaces land 16 of the pot side walls. Obviously, the spacing may be varied withand adapted to the particular heat input requirements of eachapplication. The burners 14 are conveniently mounted in a movable frame17 comprised of structural metal shapes. As shown in FIG. 2, frame 17 issubstantially rectangular and holds five vertically aligned rows ofburners 14. A corresponding frame 17 and set of burners 14 is locatedand similarly oriented on the opposite side 16 of the pot.Increased'heat input can be achieved by mounting sets of burnersdirected toward all sides and/or the bottom of the pot.

Pre-mixed quantities of gaseous fuel and air are delivered to burners 14through a distribution and supply manifold system indicated generally atM. This system comprises a large-diameter manifold 18 running across oneend and near the bottom of the furnace. The inlet end 19 of the manifold18 is connected to a source of pre-mixed gaseous fuel and air (notshown). A branch supply manifold 20 is provided on each side l5 and 16of the furnace and pot and associated with the movable frames 17 andburners 14 supported thereon.

Each branch manifold is connected to the main manifold 18 through themovable joint 2l which permits rotation of branch manifold 20 about itsaxis with respect to manifold 18. even while mixtures of gaseous fueland air are being carried by the manifolds and without any leaking ofthe mixture at the joint. Branch manifolds 20 are preferably supportedby and rest upon laterally extending arms 22. Each vertical alignment ofburners l4 contained on the frame 17 is supplied with gas from itsassociated branch manifold 20 from a plurality of longitudinally spacedoutlets therein and connecting pipes 23.

Array B of burners 14 mounted in its movable frame 17 on each side ofthe furnace is able to be swung toward and away from the large-area flatsurface sides 15 and 16 of pot 10 by pivotal swinging motion as a unitabout is lower edge and substantially about the axis of its associatedbranch manifold 20. In FIG. 2, one of the frame 17 supported burnerarrays B is shown in its upright and operating position, held there, forexample, by a simple swinging latch 24. In the position shown in FIG. 2,the burners lie in a substantially vertical plane closely spaced fromand parallel to the side walls of the pot. This relationship is seenmost clearly in the sectional view of FIG. 4.

In FIG. 3, array B of burners 14 and movable frame 17 is shown swungaway from side wall 15 of pot 10 as permitted by movable connection 21of branch manifold 20. The burner arrays are preferably arranged so thatthey can be swung and moved toward and away from the side wall of th potwhile they are in operation for easy inspection, maintenance, andrepair. This is a unique feature of furnaces embodying this inventionand contributes substantially to ease of operation and maintenance ofthe furnace.

In FIG. 2, one of the end cover plates 25 of the furnace jacket has beenremoved to reveal the pilot light assemblies, indicated generally at 26,for lighting the burner arrays on opposite sides of the pot. Pilot lightassemblies 26 comprise gas supply pipes 27, shut-off valves 28, andignition plugs 29. Any suitable ignition system may be employed andlocated as may be convenient and appropriate for the arrays andarrangement of arrays employed.

The particular burners shown in the preferred embodiment of thisinvention employ a modular construction for ease in assembling andincreased flexibility of arrangement of the total burner surface to beused. For example, each vertical burner assembly shown in FIG. 2consists of a single and a double tile burner head, bolted together toprovide a total of three burner tiles in close proximity and in a row. Areverberating screen overlies each burner tile. As shown in FIG. 3, eachvertical row of burner housing consists of three burner tiles andoverlying reverberator screens. Obviously, this invention comprehendsother combinations of burner housings having different numbers of burnertiles and which may be employed in practicing it.

FIG. 5 is an enlarged perspective and partially sectioned view ofasingle burner unit 14. The burner housing 40 comprises a casting havinga shallow, openfaced, substantially square chamber 41 facing out oneside. The open side of this chamber is closed with a radiant burnerelement 42 such as a refractory-type tile mentioned earlier. In FIG. 5,a portion of such a tile is shown in place, suitably cemented orotherwise held against the supporting ledge 43 cast in the housing. Asmall portion of reverberator screen 44 is diagrammatically indicated inFIG. 5 in a position overlying the outer surface of radiant burnerelement 42 and spaced a short distance therefrom. Such screens are wellknown in the infrared gas burner art and, as such, form no part of thisinvention. The back side of radiant burner element 42 is exposed to andsupplied with gaseous fuel and air mixture from shallow square chamber4l behind it. Chamber 4l, in turn, is supplied through an adjustableregulating and distributing orifice 45 connecting it with a relativelylarge section distribution manifold 46.

Distribution manifold 46 is located on the opposite side of the burnerhead remote from the high temperature side and radiant burner 42. Thesection of manifold 46 contained in each burner joins that of theadjacent section to form a continuous and generous distrib-.

uting passage extending the full length of each alignment of burners 14.It will be noted that the shallow chambers 4l behind each burner element42 are discontinuous and separate from and unconnected with adjacentones of such chambers. The double burner element housing, in fact, hastwo separate burner element chambers 41, each equal in area to thecorresponding chamber in the single unit.

The amount of gaseous fuel and air mixture delivered from distributionmanifold 46 of the burner heads to each individual burner 'elementchamber 41 is controlled by a plate 47 movably adjustable toward andaway from the counterbored entrance of orifice 45. Plate 47 is mountedon the end of a threaded positioning element 48 extending, forconvenience of adjustment, through and to the -outside of the bottomwall of distribution manifold 46 of each burner housing. This invention,of course, is not limited to burners employing the particular meansshown for controlling the amount of mixture delivered to the burnerheads. If the application permits, one main control valve in thedistribution manifold may be used'. Another convenient arrangement tocontrol the amount of mixture delivered is the use of a split manifoldsystem whose parts are separately controllable by means associated witheach port.

A blanket of insulating material I preferably covers the outside sufaceareas of the pot not laterally adJacent the burner arrays B. As shown inFIG. 3, the movable burner banks are bordered by insulating material Iwhich meets and provides a seal with the insulating material I lyingaround the pot. The space between the burner faces and the outsidesurface of the pot is confined by the insulating material and ventedthrough exhuast flue 49. Thus, the heat loss from the pot is minimizedand the products of combustion of the burners are prevented fromcontaminating the contents of the pot. In turn, the pollutants from thepot are prevented from being carried off with the combustion products.

The burner arrays and frame supporting the pot are preferably enclosedina sheet metal jacket, indicated generally at J. The jacket portionoverlying each burner array on opposite sides of the pot is removable topermit the lowering of the burner array to its position shownin FIG. 3.Jacket J serves as a shield to keep persons from coming in contact withthe heated burners and as a baffle to encourage the passage of coolingair upward and along the bottom side of the burners by convection.

Various arrangements of burners other than that shown in the drawingsand described above are comprehended by this invention. For example,burners might also be provided at the bottom and ends of the pot. In theparticular furnace described, the two largearea burner arrays permitmaintaining a thousand pounds of aluminum at about l,200 F. The ends andthe bottom, in general, and all areas of the pot not opposite a radiantburner surface are insulated against heat loss by insulating materialindicated generally at I in the drawings.

Those skilled in the art will appreciate that various changes andmodifications can be made in the preferred form of apparatus describedherein without departing from the spirit and scope of the invention.

I claim:

l. A furnace for heating molten substances at high temperature andcomprising a heat conducting pot for holding the substance to be heated,

an open, skeletal framework for supporting said pot,

a plurality of gas fired infrared radiating burners having a highradiant energy output, each of said burners having a manifold chamber, agas-pervious radiating element comprising a wall of said chamber, and aninlet port into said manifold chamber,

an open skeletal frame for supporting said burners mounted thereonadjacent to each other and in banks having a direct facing relationshipto that portion of said pot adjacent thereto,

said pot supporting framework and said burner supporting frame having alow heat absorbing and a low heat insulating mass and capacity,

a distribution and supply manifold system for supplying quantities ofgaseous fuel and air to said burners, said system comprising a supplyconnection to each of said inlet ports of said plurality of burners,

heat insulating material lying adjacent substantially all the exteriorof said pot not in facing relationship with said banks of burners,

whereby said pot and its contents are heated and maintained at a desiredtemperature substantially only by direct infrared radiation on portionsof the outer surface of said pot and a heat loss barrier of thermalinsulating material adjacent the remaining portions of the outer surfaceof said pot.

2. The apparatus according to claim 1 in which said pot has generallyflat side surfaces and said plurality of burners includes an array oflaterally adjacent burners ldirected at each of said generally flat sidesurfaces of said pot, said burners comprising each array having theradiating surfaces of their radiating elements facing the pot and alllying generally in a plane parallel to the surfaces faced.

3. The apparatus according to claim 2 in which said pot has a greateraverage length than width and has laterally opposite and generally flatside surfaces together comprising more than half its total surface area.

4. The apparatus according to claim 2 in which said inlet ports areadjustable individually to control the amount of gaseous fuel and airmixtures delivered to each burner from the distribution and supplymanifold system.

5. The furnace according to claim l together with sealing meansconfining the space between the radiating elements of said burners andthe pot and exhaust flue means venting the sealed and confined space topermit the products of combustion of the burners to be drawn and carriedoff without contaminating association with the molten substance in thepot.

6. The apparatus according to claim 2 in which said distribution andsupply manifold system includes a branch manifold associated with andconnected to each of said arrays of burners, and said arrays andassociated branch manifolds-each being mounted on a movable tween toccommodate the swinging motion of its associated burner array evenduring operation of the burners.

1. A furnace for heating molten substances at high temperature andcomprising a heat conducting pot for holding the substance to be heated,an open, skeletal framework for supporting said pot, a plurality of gasfired infrared radiating burners having a high radiant energy output,each of said burners having a manifold chamber, a gas-pervious radiatingelement comprising a wall of said chamber, and an inlet port into saidmanifold chamber, an open skeletal frame for supporting said burnersmounted thereon adjacent to each other and in banks having a directfacing relationship to that portion of said pot adjacent thereto, saidpot supporting framework and said burner supporting frame having a lowheat absorbing and a low heat insulating mass and capacity, adistribution and supply manifold system for supplying quantities ofgaseous fuel and air to said burners, said system comprising a supplyconnection to each of said inlet ports of said plurality of burners,heat insulating material lying adjacent substantially all the exteriorof said pot not in facing relationship with said banks of burners,whereby said pot and its contents are heated and maintained at a desiredtemperature substantially only by direct infrared radiation on portionsof the outer surface of said pot and a heat loss barrier of thermalinsulating material adjacent the remaining portions of the outer surfaceof said pot.
 2. The apparatus according to claim 1 in which said pot hasgenerally flat side surfaces and said plurality of burners includes anarray of laterally adjacent burners directed at each of said generallyflat side surfaces of said pot, said burners comprising each arrayhaving the radiating surfaces of their radiating elements facing the potand all lying generally in a plane parallel to the surfaces faced. 3.The apparatus according to claim 2 in which said pot has a greateraverage length than width and has laterally opposite and generally flatside surfaces together comprising more than half its total surface area.4. The apparatus according to claim 2 in which said inlet ports areadjustable individually to control the amount of gaseous fuel and airmixtures delivered to each burner from the distribution and supplymanifold system.
 5. The furnace according to claim 1 together withsealing means confining the space between the radiating elements of saidburners and the pot and exhaust flue means venting the sealed andconfined space to permit the products of combustion of the burners to bedrawn and carried off without contaminating association with the moltensubstance in the pot.
 6. The apparatus according to claim 2 in whichsaid distribution and supply manifold system includes a branch manifoldassociated with and connected to each of said arrays of burners, saidarrays and associated branch manifolds each being mounted on a movableframe pivotally supported for swinging motion generally about one sidethereof and toward and away from said pot, each of said branch manifoldshaving a connection with said system which remains substantiallygas-tight while permitting relative movement therebetween to accommodatethe swinging motion of its associated burner array even during operationof the burners.